Correlation of Adenosine Triphosphate Levels in Chara corallina with the Activity of the Electrogenic Pump

Abstract

The effect of a number of inhibitors on the ATP level in single cells of C. corallina was measured using the luciferin-luciferase assay. The uncouplers of phosphorylation, carbonyl cyanide m-chlorophenyl hydrazone and 2,4-dinitrophenol, and the ATPase inhibitors, dicyclohexylcarbodiimide and diethylstilbestrol, all caused a marked reduction of the ATP level. These inhibitors also produced a large increase in the membrane resistance and a depolarization of the membrane potential to the diffusion potential. This is consistent with the plasmalemma containing an ATP-dependent electrogenic pump that provides the primary conductance through the membrane. Ethyl-3-(3-dimethylaminopropyl)carbodiimide, which depolarizes the membrane potential, has no effect on the ATP level and does not increase the membrane resistance. This inhibitor apparently does not enter the cell but may act by affecting the permeability of the membrane. Neither darkness nor 3-(3,4-dichlorophenyl)-1,1-dimethylurea lowers the ATP level and while neither has much effect on the membrane potential, both cause a similar increase in resistance in comparison with the control in the light. The weak acid, 5,5-dimethyloxazolidine-2,4-dione, and the weak base, NH3, do not affect the ATP level significantly but they have effects on the electrogenic pump that are consistent with their postulated effects on the cytoplasmic pH if H+ is the substrate for the pump.